Studies will continue on the physiological mechanisms of mammalian hibernation using principally ground squirrels, dormice and Turkish hamsters as experimental animals. Temperature regulation of hibernating animals exposed to potentially lethal cold ambient temperatures will be explored using oxygen consumption as the indicator of metabolic rate. An increase in metabolic rate proportional to the decline in ambient temperature will indicate that temperature regulating mechanisms are functioning. Similar measurements will be made using a thermode to manipulate brain temperature alone. The results will be compared with those obtained from hibernating animals with lesions in the preoptic-hypothalamic area. Using recording from single units a systematic study will be started to attempt to locate the area of the brain used to regulate temperature in the hibernating animal. The bursts of muscle action potentials which always accompany an effective peripheral stimulus in the hibernating animal will be examined in more detail to determine if the muscle action potential is a necessary concomitant to the appearance of an evoked cortical potential. By serial transections of the brain, we will attempt to determine what level of the CNS is influencing the sensitivity to peripheral stimuli in the hibernating animal. We will continue observations on our colony of Turkish hamsters and begin pilot experiments on the influence of the endocrines on hibernaton, one experiment involving the effect of prolactin injected at various times during the circadian cycle.